Coronary arteries provide blood and nutrients to the heart muscle. The arteries are subject to atherosclerosis or hardening of the arteries. Vascular regions have plaques formed within, resulting in stenosed regions having reduced cross-sectional area. The reduced area causes a reduction in transport of blood, oxygen, and nutrients which can result in angina, myocardial infarction and death.
A commonly used method for treating atherosclerosis is Percutaneous Transluminal Coronary Angioplasty (PTCA). PTCA includes insertion of a balloon catheter through an incision in the femoral artery near the groin, advancement of the balloon over the aortic arch, further advancement within the selected coronary artery, continuing until the balloon portion is placed across the stenosed region. The balloon is inflated, widening the narrowed vessel region.
After catheter withdrawal, significant vessel reclosure may develop. The reclosure may occur within hours or days of dilation, an "abrupt reclosure." When reclosure does occur, however, it more commonly occurs progressively, within six months of the angioplasty. The gradual reclosure is referred to as "restenosis", and largely negates the dilatation treatment. More highly stenosed vessel regions have a greater chance of becoming restenosed.
One approach to dealing with restenosis utilizes stents which are short tubular sections having a lumen therethrough, placed across the recently dilated vessel region. Stents can be either self-expanding or balloon-expandable. Stents are normally left in place indefinitely.
Stents, as any permanently implanted device, may possibly cause long term problems. As the stent is forever pushing radially outward against the vessel wall, the wall may be adversely affected over long time periods. Stent ends, which push radially outward, are adjacent to soft tissue which can be irritated by the stent end. Some believe the stent could promote restenosis in the region immediately beyond the stent ends. For this reason, the vessel may develop a new stenosed region adjacent either stent end. Stents commonly have wire mesh or spring structures, with openings in the stent walls. "Intimal hyperplasia", rapid tissue growth through stent openings has also been reported. While the exact mechanism of restenosis is not understood, it is believed that the vessel narrowing is due more to cellular growth mechanisms than to an elastic rebound mechanism.
Use of radiation to kill and inhibit growth of cancerous cells is well known. The use of radiation to inhibit restenosis has been proposed. U.S. Pat. No. 5,059,166 (Fischell et al.) proposes using a radioactive stent. Radioactive stents are indefinitely placed devices, with the possible irritating effects of stents. Furthermore, as stents are commonly formed of open structures such as springs or meshes, portions of vessel walls are exposed to radiation while other vessel areas more remote to stent wires, are exposed to much less radiation, if any. Further, the vessel cross section in a stenosed area may not conform to the stent shape and thus, the dose of radiation may vary due to proximity of the radioactive source to the vessel wall at any point.
Use of a catheter having a radioactive source on the distal end has been proposed in U.S. Pat. No. 5,199,939 (Dake et al.). The catheter must be held in place during the entire therapy, which is considerably shorter than the months long period over which restenosis is believed to occur. Any radiation delivered must be delivered within the short period the catheter tip is in place. The radiation dosage may be greater than that required if the exposure were more closely matched to the restenosis period. Centering the radioactive source within the vessel may be difficult, providing a greater dosage at the closer vessel wall than the further. The radiation source must be capable of reaching from catheter center, through any fluid, to vessel interior walls and beyond. This may require a more energetic, further penetrating source compared to that required if the radiation could be held directly and evenly over the vessel walls.
Use of adhesives in place of sutures in surgery is known. See, for example, "Histotoxicity of Cyanoacrylate Tissue Adhesives", 116 Arch Otolaryngol Head Neck Surg 546 (May 1990). See also "A New Biological Glue from Gelatin and Poly(L-glutamic acid)", 31 J. Biomedical Materials Res 157 (1996).
What is desirable and has not heretofore been provided is a method for inhibiting restenosis using radiation applied evenly, over long periods, without requiring stent placement. What would also be desirable is a method allowing for stent placement while inhibiting restenosis through stent walls and beyond the ends of the stent.